Slotted prismatic antenna



J. E. PAUCH SLOTTED PRISMATIC ANTENNA Sept 18, 1951 2 Sheets-Sheet 1Filed Dec. 27, 1946 WN vN w A i M fi l zr z kfaadb BY )F /ww/n,

' ATTOEQNEY TOR p 1951 J. E. PAUCH 2,568,560

SLOTTEJD PRISMATIC ANTENNA 2 Sheets-Sheet 2 Filed Dec. 27, 1946INVENTOR.

Patented Sept. 18, 1951 SLOTTED PRISMATIC ANTENNA John E. Pauch,Montreal, Quebec, Canada, assignor to Radio Corporation of America, acorporation of Delaware Application December 27, 1946, Serial No.718,791

2 Claims. 1

The present invention relates to antennas and more particularly to ultrahigh frequency antennas.

An object of the present invention is to provide an antenna elementhaving broad band characteristics.

Another object of the present invention is to provide an antenna capableof radiating substantially pure horizontally polarized waves.

Another object of the present invention is to radiate high frequencyenergy with highly uniform field intensity in all directions in thehorizontal plane.

Still another object of the present invention is the provision of asimple low cost, broad band antenna suitable for use in broadcasttransmission.

The foregoing objects and others which may appear from the followingdetailed description are attained by providing a radiator element in theform of a hollow sheet metal prism of triangular, square or otherpolygonal cross section or in the form of a hollow sheet metal cylinder.The prism or cylinder is provided with two or more equally spacedlongitudinal slots about its circumference, The antenna thus formed isfed with single phase radio frequency energy across the slots with allof the slots connected in parallel in such a way that all the currentsaround the exterior of the antenna are in the same direction.

The present invention will be more fully understood by reference to thefollowing detailed description which is accompanied by a drawing inwhich:

Figure 1 illustrates in elevation an embodiment of the presentinvention, while Figure 2 illustrates a cross sectional view of theantenna taken along line 2,2 of Figure l, and

Figures 3, 4 and 5 are fragmentary views showing modifications ofdetails of the antenna.

The antenna of the present invention consists of a hollow sheet metalbody ID of generally prismatic or cylindrical form. The embodiment shownin the drawing is hexagonal in cross section but a circular or otherpolygonal cross section may be used if desired. The antenna of thepresent embodiment is composed of a plurality of flat planar surfaces H,l2, I3, 14, I5 and I6 arranged in a hexagonal formation. Preferablyadjacent faces such as i2l3, I l-45 and l8ll are continuous leavingslots l1, l8 and [9 at alternate corners of the hexagon. The metallicsheets, where they are adjacent to slots ll, l8 and I9, are preferablyprovided with inturned flanges to provide means for clamping thestructure together and also to provide for ready connection of thetransmission line across the slots. The flanges 20 are maintained inparallel insulated relationship one with the other by means of clampingbolts 22 passing through suitable apertures 24 and 26 through theflanges 20. An insulating spacer 25 maintains the spacing between theflanges 20. The bolts 22 may be insulated from flanges 20 by shoulderedinsulating washers 28. As shown more clearly in Figure 1 three or moresuch clamping means may be provided along each of the longitudinal slotsI7, l8 and I9. For embodiments where the overall length of the antennais of the order of a half wavelength or more it is necessary that theinsulated construction described be provided at the center clampingpoint only, the spacers at the ends of the radiator being constructed ofconducting material, The voltage across the slots at the ends of theradiator is, for such lengths, so low that there is no necessity forproviding insulation at the ends. Furthermore, an all-metal clampingstructure at each end increases the mechanical rigidity of thestructure. If desired, the upper end of the antenna may be closed in bya hexagonal conductive plate whereby the structure is strengthened andforeign matter kept out of the interior of the structure. Similarclosing means may be also provided at the bottom to which the desiredsupporting structure may be attached. In order to allow convenientaccess to holes 24 and 26 through which the clamping bolt 22 passes forassembly and for inspection, access holes 29 may be provided in the flatfaces of the antenna.

The antenna as so far described is ordinarily mounted vertical with atransmission line TL passing up into the interior from the base. Atsubstantially the midpoint of the antenna the transmission line TL isconnected in parallel relationship to slots I1, I8 and I9 by shortsections of two-wire transmission line TLl, TL2 and TLs. As indicated bythe arrows in Figure 2 the connection is in such sense that the exteriorcurrents flow in the same direction around the antenna. While I haveshown the transmission lines as being connected to the midpoint of theantenna, other points along the individual slots may be utilized ifdesired. In some cases the slots may be fed at one end thereof.

The dimensioning of the antenna is not critical since the diameter maybe chosen anywhere between the limits of wavelength and /4 wavelength atthe midband operating frequency. The

length of the antenna is not critical but may be as short as 6wavelength or as long as one or more wavelengths. The ends of the slotsl1, l8 and 19 should preferably not be short circuited unless theoverall length of the antenna is of the order of a half wavelength ormore with the feed point at substantially the center of the radiator.

The antenna arranged and energized as described above has an essentiallyuniform unidirectional current circulating circumferentially about theexterior. The resulting field produced is to a high degree free fromvertical polarization components and has a high degree of uniformityabout the vertical axis. There is no radiation along the axis of theradiator. r

The input impedance characteristics of the radiator are such that it maybe readily adapted to operate over a wide frequency range withoutreadjustment of the antenna system. The-broad band characteristicsof-the antenna are determined somewhat' by the length of the cylinder,the longer the antenna the greater the bandwidth. The uniformity of thefield in the horizontal plane depends upon the number of thelongitudinal slots and on the diameter of the antenna. Apparently theoptimum number of slots is three and a more uniform radiation pattern isobtained with the smaller diameters. The input impedance of the antennais dependent upon the number of longitudinal slots, the diameter of theantenna, the capacity between the flanges 20 and, to some extent, uponthe length of the cylinder. Ordinarily the width of the slots ll, 18 andlii'and/or the width of the flanges 20 is adjusted to make the radiatorresonant at midpoint frequency; Increasing the slot width ordecreasingthe widths of flanges 20 increases the resonant frequency. Thecross sectional shape of the antenna has practically no effect on itscharacteristicsas long as the departure from a generally circularformation is not too great.

Tests on an embodiment of the antenna described above approximately 60inches in length and 18 inches across corners indicated that asatisfactorily circular radiation pattern and a substantially constantinput impedance was obtained over a frequency range of from 112 t 118megacycles.

In Figures 3 and 4 I have shown fragmentary views of modifications oftheform of the invention' described above. Figure 4 shows in section asolid insulator 25 having studs 52 screwed into tapped holes in eachendof the insulator. This construction may be used instead of theinsulator 25, insulating washers 28 and clamping bolt 22 of Figure 2.Thus the studs 52 and nuts 24 need not be insulated from the flanges 20.

This arrangement may, in many cases be simple, less expensive and morerigid than the arrangement of Figure 2.

Figure '3 shows in elevation, from the interior 'of the antenna anarrangement of a number of insulators 25 along on of the slots which hasbeen actually used. As shown here and in Figure '5 the conductors oftransmission line TL1 are connected to flanges 20 by bolts 53 andclamping 'nuts 54. at substantially the midpoint of slot l1, if desired'connection may be made near one end or the other, if the ends areinsulatedas indicated in Though in this figure they are shown Figure 3.

Also if desired, the conductors of the two wire transmission lines, asindicated with respect to line TL1 in Figure 5, may be located within aI 4 shielding tube 56, maintained in alignment about the conductors byinsulating spacers such as that shown at 55.

While I have, illustrated a particular embodiment of the presentinvention, it should be clearly understood that it is not limitedthereto since many modifications may be made in the several elementsemployed and in their arrangement without departing from the-spirit andscope of the invention.

What is claimed is:

1. A high frequency antenna including a plurality of elements of flatconductive material arranged to form a substantially closed prismaticmember, the over-all length of said member being substantially a halfWavelength at the midband operating frequency, and the dimensions ofsaid member transverse to the longitudinal axis thereof being betweenone-tenth and one-quarter wavelength at the midband operating frequency,said elements having rectilinear edges spaced to form a number of slotsin said member, there being parallel inturned flanges along saidrectilinear edges, and means to couple a two-conductor transmission linedirectly to said antenna, one of said conductors being connected tocorresponding slots at said rectilinear edges of all of said slots andthe other conductor being directly connected to the remaining edges tocause the instantaneous currents to flowin the same direction about theperimeter of said member.

2. A high frequency antenna including a plurality of sheets of fiatconductive sheet material having rectilinear edges, said sheets beingbent to form inturned flanges along said rectilinear edges and beingarranged to form a sub stantially closed prismatic member, the overalllength of said member being substantially a half wavelength at themidband operating frequency, and the dimensions of said membertransverse to the longitudinal axis thereof being between one-tenth andone-quarter Wavelength at the midband operating frequency, some of saidrectilinear edges being spaced to form three longitudinal slots in saidprismatic member, and means to couple a two-conductor transmission linedirectly to said antenna, one of said conductors being connected tocorresponding rectilinear edges of all of said slots and the otherconductor being directly connected to the remaining edges to cause theinstantaneous currents to flow in the same direction about the perimeterof said member.

JOHN E. PAUCH.

REFERENCES CITED Thefollowing references are of record in the 'file ofthis patent:

UNITED STATES. PATENTS Number; 7 Name Date 2,206,923 Southworth July 9,1940 2,234,293 Usselman Mar. 11, 1941 2,238,770 Blumlcin Apr. 15, 19412,405,242 Southworth Aug. 6, 1946 1 2,411,872 Feldman et a1 Dec. 3, 19462,414,266 Lindenblad Jan. 14, 1947 2,434,253 Beck Jan. 13, 1948 OTHERREFERENCES Radio, July 1946, pages 14 and 15. F. M. and Television,September 1946, pages 45 to 47. v

